Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$221.47	3.671%	$229.6002	$229.60	$229.60	$229.60
Purchase #2	$32.78	9.346%	$35.8436	$35.84	$35.85	$35.80
Purchase #3	$39.27	13.320%	$44.5008	$44.50	$44.50	$44.50
Purchase #4	$60.29	9.488%	$66.0103	$66.01	$66.00	$66.00
Purchase #5	$230.86	10.846%	$255.8991	$255.90	$255.90	$255.90
Purchase #6	$216.39	11.806%	$241.937	$241.94	$241.95	$241.90
Purchase #7	$6.82	10.840%	$7.5593	$7.56	$7.55	$7.60
7 purchase totals =	$807.88		$881.3503	$881.35	$881.35	$881.30